1. Season the chuck roast generously with salt and pepper.
2. In a large skillet, heat the olive oil over medium-high heat. Sear the roast on all sides until browned, about 4-5 minutes per side.
3. Transfer the roast to the slow cooker.
4. In the same skillet, add the chopped onion and garlic. Sauté until softened and fragrant, about 3 minutes.
5. Add the onion and garlic to the slow cooker, along with the chopped carrots, parsnips, and potatoes.
6. In a mixing bowl, combine the beef broth, red wine (if using), tomato paste, Worcestershire sauce, thyme, and bay leaves. Pour over the meat and vegetables in the slow cooker.
7. Cover and cook on low for 8-10 hours or on high for 4-6 hours, until the meat is tender and the vegetables are cooked through.
8. Remove the thyme sprigs and bay leaves before serving.
9. Shred the meat with two forks, if desired, and stir it into the juices. Serve hot.

Variations & Tips
Feel free to mix up the root vegetables based on what you have on hand – sweet potatoes, celery root, or turnips would all be great additions. For a slightly different flavor profile, try adding a splash of balsamic vinegar along with the broth. And if you prefer a thicker sauce, you can remove some of the cooking liquid at the end and thicken it with a slurry of cornstarch and water before serving.